The invention relates to a method of taking samples from pig-iron melts, e.g. from a blast-furnace tapping spout or a normal ladle or a torpedo ladle, the melts solidifying to form a homogeneous white-iron structure, in which the sample solidifies in the sample-taker cavity in the presence of a small quantity of an additive.
There are practical difficulties in taking samples of pig-iron which solidify into a homogeneous white-iron structure (white cast iron). Unless special methods are used, pig-iron solidifies in a structure which has a blackish colour as a result of graphite precipitation. Such samples are unsuitable for complete spectrometric pig-iron analysis, since the samples for analysis must solidify into a white, homogeneous structure which is visible at a fracture face.
In addition, if there are graphite precipitates in the sample, the analysis may not be reproducible and the sample-taking may not be representative; this is particularly important at the end of the heat. Such samples, containing a number of graphite precipitates at the analytical surface, are also unsuitable for quantitative analysis.
Attempts have long been made to control the solidification of pig-iron samples to ensure that they solidify into a homogeneous white-iron structure. One prior-art method is based on the direct conversion of blast-furnace pig-iron into a low-alloy pig-iron at the moment of sampling. In the method, "carbide-forming elements", i.e. chromium and vandium, are added to the sample; their effect is based on the fact that the carbon is bonded, thus preventing the precipitation of graphite, and the sample solidifies into a white-iron structure. The known method has disadvantages in that elements are added and may include the elements under analysis. In addition, the method requires a spoon, in which the added elements are dissolved and mixed with the sample.
French Patent Specification No. 2 171 627 discloses a device for taking pig-iron samples and adapted to solidify the sample into a homogeneous white-iron structure. In the process a given quantity of an additive--pulverulent tellurium--is wrapped in metal foil, e.g. aluminium paper, and placed in the device so that the liquid pig iron dissolves the additive before solidifying.